Capsule production promotes Group B Streptococcus intestinal colonization.

Area of Science:

• Microbiology
• Infectious Diseases
• Vaccinology

Background:

• Late-onset Group B Streptococcus (GBS) disease in infants often follows gastrointestinal colonization.
• GBS capsular polysaccharide is a key virulence factor, with vaccines targeting specific serotypes in development.
• The role of specific GBS serotypes in initial gastrointestinal colonization remains largely uncharacterized.

Purpose of the Study:

• To investigate the influence of GBS capsular polysaccharide production on gastrointestinal colonization in a murine model.
• To compare the colonization fitness of GBS strains with different capsular serotypes (Ia vs. III).

Main Methods:

• Utilized isogenic GBS strains (capsule-producing vs. acapsular) derived from serotype Ia strain A909 in a murine model.
• Assessed colonization persistence in monocolonization experiments.
• Determined competitive indices during cocolonization to evaluate the advantage of capsule production and specific serotypes.

Main Results:

• Capsule production significantly enhanced GBS persistence in the murine gastrointestinal tract compared to acapsular mutants.
• The capsule-producing GBS strain outcompeted its acapsular counterpart in cocolonization experiments (geometric mean competitive index = 8).
• GBS serotype Ia demonstrated a competitive advantage over serotype III in the A909 strain background (geometric mean competitive index = 2.5).

Conclusions:

• Polysaccharide capsule production is crucial for efficient GBS gastrointestinal colonization *in vivo*.
• Specific GBS serotypes, such as Ia, possess enhanced colonization fitness compared to others like III.
• The murine model is effective for studying the impact of GBS capsule types on colonization and potential disease outcomes.